Gun drills or reamers of the type with which the present invention is concerned comprise a cutting tool for drilling, reaming, and other machining operations that require a comparatively long tool shaft or shank having a cutting end located at an appreciable axial distance forwardly from its bushing support and its rearward or driven end, which latter is secured to power means for simultaneously rotating and reciprocating the tool during a cutting operation.
The cutting end of the tool may reciprocate axially across a work piece during a cutting operation, or might necessarily be located at some distance axially from its bushing support, and is thus unsupported at least throughout the comparatively long axial extent required for the reciprocating movement. Because of the long unsupported axial extent of the cutting tool, such tools are referred to as gun drills or reamers, although their use is not limited to machining gun barrels. In fact they are commonly used in many industrial machining applications requiring a cutting tool having the above mentioned characteristics.
Customarily, gun drills or reamers are powered by coaxial inner and outer power driven spindles keyed together for rotation as a unit, wherein the inner spindle is also movable axially while rotating to effect the desired cutting operation. Also the inner spindle coaxially supports the rearward portion of the tool shank during the desired rotational and axial cutting movement. The outer spindle is customarily secured to a coaxial bushing adapter that extends forwardly of the inner spindle and around the shank of the cutting tool for an axial distance at least equal to the reciprocating movement and supports a conventional bushing at its forward end for supporting a rotatable and reciprocating tool shank.
Important objects of the present invention are to provide an improved compact quick change tool holder for coaxially supporting the shank of the gun drill or reamer within high precision tolerances for high speed operations that may exceed 8000 rpm; and to provide such a holder having improved radial flange mounting and coaxial pilot means cooperable with the customary inner power driven spindle for attachment therewith in high precision piloted relationship; and which also coaxially supports the rearward portion of the tool shank in spline driving engagement.
Other objects are to provide such a tool holder having improved means for actuating a radially contractable tool clamping split collet for readily and quickly releasably clamping and supporting the tool shank in high precision coaxial alignment forwardly of the coaxial spline driving attachment, and wherein by virtue of the spline driving engagement, the collet is merely required to provide high precision coaxial support for the tool shank without providing driving torque.
Heretofore it has been conventional to utilize a conical split collet movably axially into mating engagement with a conical collet seat for constricting the collet radially around the tool shank, wherein the collet supports the tool shank coaxially and also provides the driving force for rotating the shank during a cutting operation, whereby in consequence of high speed and high torque operation, the collet often spins on the tool shaft, rapidly wearing and requiring replacement of both the collet and shaft.
Another object is to provide simple and effective means for moving the tool clamping collet axially to and from clamping engagement with a tool shank, comprising a non-axially movable collar rotatable on a cylindrical portion of the holder. The collar is also in screw threaded engagement with an axially movable but non-rotatable nut secured to the collet for moving axially therewith. Upon rotation of the collar, the non-rotatable nut and attached collet are positively moved axially to and from the aforesaid clamping engagement with the tool shank.
Limited lost motion between the collet and the actuating nut is provided by the attachment therebetween so that as the nut is moved axially to move the collet into clamping engagement with the tool shank, the collet is free to align itself precisely with a mating coaxial conical surface of the tool holder regardless of slight deviations of the nut from coaxial alignment with the collet, as might result by reason of lax tolerances in the screw threaded engagement between the collar and the nut. Thus, without recourse to precise machining of the nut and its threaded engagement with the collar, the desired high precision coaxial support for the tool is assured to enable high speed high precision machining.
Other objects are to provide the nut, that may be detachably secured to the collet, with diametrically spaced axially extending notches that ride axially along non-rotatable prongs or retaining projections of the tool holder to prevent rotation of the nut with the collar. Thus upon rotation of the collar, the screw threaded engagement between the collar and nut immediately moves the non-rotatable nut and attached collet axially to and from clamping engagement with the tool shank, depending upon the direction of rotation of the collar, whereby rotational slipping of the collet within its mating conical recess within the tool holder is avoided; and to provide the collar and nut with interengaging screw threads such that rotation of the collar to move the collet into clamping engagement with the tool shank will be opposite the normal direction of rotation of the tool in the cutting operation, whereby the cutting operation tends to enhance the gripping action of the collet.
Another object is to provide improved means for enabling rotation of the collar on the cylindrical surface of the tool holder while preventing axial movement, comprising a radially resilient retention ring secured within confronting anular grooves in the collar and cylindrical surface upon which the collar is rotatable. The axially spaced sides of the ring and its retaining grooves comprise parallel planes normal to the axis of the tool holder and shank, whereby axial force transmitted between the ring the side walls of the groove is distributed uniformly around the entire circumference of the ring, minimizing wear between the parts and enabling close confinement of the ring between the side walls of the grooves.
Another object is to provide the collar with annularly arranged beveled gear teeth engageable with mating beveled gear teeth of a wrench rotatable about an axis normal to the axis of the holder, whereby the wrench is insertable through a comparatively small radially opening window in the bushing adapter to enable rotation of the collar and clamping and releasing of the cutting tool.
Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.